The payments continued through 2009, the newspaper reported, including tens of thousands of dollars paid to Rajoy.

"I have nothing to hide. I am not afraid of the truth," said Rajoy, long a party leader who became prime minister in December 2011.

He announced that his income tax statements and declaration of personal wealth would be posted next week on the prime minister's website.

"I am personally committed, and I commit the party to use the maximum transparency in this matter."

He also acknowledged -- in the speech to the party's executive committee, hurriedly convened for a special meeting -- the damage that the allegations have done after several days as top news across all Spanish media, with prominent coverage abroad, as well.

During Spain's deep economic crisis, with austerity cuts, tax hikes and 26% unemployment, Rajoy said, "We can't permit that Spaniards, whom we are asking to make sacrifices, could have the impression that were are not up to strictest ethical standards."

El Pais reported that the money came into Popular Party coffers from construction firms and other businesses and was used for various purposes, including secretive cash payments to party officials.

El Pais reported that the individuals and companies cited in the alleged documents have denied giving or receiving party funds in an off-the-books manner.

A former Popular Party treasurer, Luis Barcenas, is under investigation for a Swiss bank account, and Rajoy took pains to distance himself and the party from Barcenas.

"We learned of the existence of 22 million euros in a private bank account in a Swiss bank," Rajoy said. "This has nothing to do with the Popular Party. The Popular Party does not have, nor has it had, bank accounts in a foreign country."

El Pais headlined its story Thursday that started the allegations, "The secret papers of Barcenas."

That same day, another newspaper, ABC, headlined its story: "Luis Barcenas accuses the Popular Party leadership of having collected in B," the letter Spaniards typically mention when referring to secretive cash payments under the table with the aim of avoiding taxes.

"I didn't come into politics to earn a lot of money," Rajoy said Saturday. "I came into politics and have earned less money, but it so happens that money is not the most important thing for me. For others, I don't know."

The party later Saturday issued an internal report saying that its top leaders, from 1995 to the present, have signed sworn statements or will do so in the coming days that attest they have all paid their taxes properly and have not received any improper cash payments.

Rajoy earlier also ordered an external audit of the party's finances.

Rajoy warned his political adversaries that the party would defend itself and that their efforts to hurt the party and the government would not succeed.

Hundreds of protesters on Thursday and Friday nights demanded Rajoy's resignation in demonstrations near the ruling party's headquarters, guarded by riot police.

Rajoy is scheduled to fly to Berlin on Monday for meetings with German Chancellor Angela Merkel, focused on economic issues. Some analysts said he chose to address the scandal on Saturday at home, in hopes that it would not follow him to his meetings in Germany.